Large areas of ancient Dacia, which were populated early in the First Iron Age by Thracian people, were affected by a massive migration of Iranian Scythians moving east to west during the first half of the first millennium BCE. They were followed by a second equally large wave of Celts migrating west to east.^[105] Celts arrived in northwestern Transylvania in around 400–350 BCE as part of their great migration eastwards.^[106] When Celtic warriors first penetrated these territories, the group seem to have merged with the domestic population of early Dacians and assimilated many Hallstatt cultural traditions.^[107]

In the vicinity of 2nd century BCE Transylvania, the Celtic Boii settled in the northern area of Dunántúl, in modern-day southern Slovakia and in the northern region of Hungary around the centre of modern-day Bratislava.^[108] Boii tribal union members the Taurisci and the Anarti lived in northern Dacia with the core of the Anarti tribe found in the area of the Upper Tisa. The Anartophracti from modern southeast Poland are considered part of the Anarti.^[109] Scordiscan Celts dwelling southeast of the Iron Gates of the Danube may be considered a part of the Transylvanian Celtic culture.^[110] A group of Britogauls also moved into the area.^[111]

Celts penetrated first into western Dacia, then as far as north-west and central Transylvania.^[112] A large number of archaeological finds indicate a sizeable Celtic population settling for a long period among the natives.^[113] The archaeological evidence shows that these Eastern Celts were absorbed into the Geto-Dacian population.^[114]